The invention relates to a method for producing a turbine rotor of an exhaust gas turbocharger, wherein the turbine rotor is composed of a turbine wheel with a hub and turbine blades extending from the hub, as well as a shaft. The invention further relates to the use of a turbine rotor.
The response and the torque build-up, respectively, of an internal combustion engine supercharged by an exhaust gas turbocharger depend largely on the mass moment of inertia of the rotor assembly of the exhaust gas turbocharger and in particular on its turbine rotor. The major part of the mass moment of inertia is generated by the mass of the turbine wheel, which is part of the turbine rotor. The smaller the turbine wheel is, the quicker can the torque build-up take place. Accordingly, the response of the internal combustion engine can be improved by reducing the mass of the turbine wheel. One approach to reduce the mass of the turbine wheel is the replacement of the typically employed nickel base alloy, which has a density of about 8 g/cm3, with a different material having a lower density. The material used for the turbine wheel has ideally high temperature properties, especially at temperatures exceeding 800° C., comparable to those of nickel-based alloys. However, materials which have the above properties, i.e. in particular a low density and good high temperature properties, are typically not resistant to oxidation at the temperatures of more than 800° C. that are present in the exhaust gas turbocharger due to the flow of hot exhaust gas from the internal combustion engine. This means that these materials are subjected to an oxidation process during the operation of the exhaust gas turbocharger, which adversely affects the surface of the turbine wheel. This applies in particular to the turbine blades, which are directly exposed to the hot exhaust gas, but in principle also to the hub on which the turbine blades are located.